1. Field of the Invention
The present invention is generally related to a lubrication circuit for an engine and, more particularly, to a lubrication system that efficiently uses an internal structure of a rotating shaft as a dual fluid path for lubricating oil.
2. Description of the Prior Art
Those skilled in the art of internal combustion engines know that lubrication of certain regions of the engine, where one surface slides on another surface, is crucial to maintaining the proper operation of the engine. Many types of lubrication circuits are well known to those skilled in the art.
U.S. Pat. No. 4,896,634, which issued to Kronich on Jan. 30, 1990, describes a phase timed camshaft spray lubrication system. The lubrication system, which is for an internal combustion engine, causes lubricating oil to flow through a central bore of a camshaft, and the camshaft sprays oil into a journal bearing. The crankshaft and camshaft are configured so that they are in phase, whenever the camshaft is closest to the crankshaft during a rotation, the camshaft sprays oil into the internal bearing. Since the crankshaft has twice the rotational velocity of the camshaft, two spray holes are provided in the camshaft so that a spray hole supplies oil on each cycle of the crankshaft rotation.
U.S. Pat. No. 5,524,581, which issued to Rush et al on Jun. 11, 1996 describes an outboard motor with an improved engine lubrication system. An internal combustion engine comprises a cylinder block which defines a cylinder, a crankshaft bearing supported at least in part by the cylinder block, a crankshaft which is rotatably supported by the crankshaft bearing, a piston slidably housed in the cylinder, a connecting rod having one end connected to the piston and having an opposite end connected to the piston and having an opposite end connected to the crankshaft, a cylinder head mounted on the cylinder block, a camshaft at least partially supported by the cylinder head for rotation relative thereto, and an oil pump having an inlet. It further comprises a first oil conduit communicating between the oil pump outlet and the crankshaft bearing, an oil filter communicating with the first oil conduit for filtering oil only in the first conduit, and a second oil conduit communicating between the oil pump outlet and the camshaft, oil in the second oil conduit being unfiltered between the pump outlet and the camshaft.
U.S. Pat. No. 5,996,561, which issued to Watanabe on Dec. 7, 1999, describes a vapor separator for an outboard motor. The outboard motor has a cowling and a water propulsion device. An internal combustion engine is positioned in the cowling and arranged to propel the water propulsion device. A crankshaft of the engine is supported for rotation with respect to the engine block and is located in a first chamber. A camshaft is supported for rotation with respect to the engine block and is located in a second chamber. The engine further includes a lubrication system for the lubrication of the crankshaft and the camshaft. A lubrication collection area is located on the bottom side of the engine for the gravitational collection of engine lubrication fluid from the first chamber and the second chamber.
U.S. Pat. No. 5,027,762, which issued to Tokuyama et al on Jul. 2, 1991, describes a lubrication system for a multi-cylinder engine. The system has a valve drive mechanism equipped with a row of hydraulic valve lash adjusters installed in a cylinder head of an engine block of an engine and a camshaft with journals which is disposed over the cylinder head and is attached, at one end thereof, with a camshaft pulley coupled to a crankshaft pulley by a belt. The lubrication system includes a main oil gallery extending lengthwise in the engine body, a lash adjuster oil gallery formed in the cylinder and extending along the row of hydraulic valve lash adjusters and a camshaft oil gallery formed in the cylinder head and extending parallel to the lash adjuster oil gallery.
U.S. Pat. No. 6,170,448, which issued to Asakura on Jan. 9, 2001, describes a variable valve timing apparatus. It includes a phase adjuster for adjusting the rotational phase of the camshaft relative to a crankshaft and a lift adjuster for axially moving the camshaft. The phase adjuster has a timing pulley rotated synchronously with the crankshaft and a housing fixed to the timing pulley. A vein rotor rotating synchronously with the camshaft is arranged in the housing to define a first pressure chamber and a second pressure chamber in the housing. Hydraulic fluid is delivered to the first and second pressure chambers through oil conduits to rotate the vein rotor with respect to the housing and change the rotational phase of the camshaft relative to the crankshaft. The oil conduits extend through the timing pulley. This prevents the axial movement of the camshaft from affecting the hydraulic pressure of the pressure chambers. Accordingly, the valve timing is varied accurately.
U.S. Pat. No. 5,090,375, which issued to Hudson on Feb. 25, 1992, describes a valve gear oiling system for an overhead camshaft engine. A single cylinder, overhead cam, internal combustion engine lubrication system where lubricating oil is pumped from a crankcase oil sump through oil passages to the upper bearings of the crankshaft and camshaft is disclosed. The oil leaks from the bearings, adheres and flows down the shafts which is flung by rotation thereby lubricating the cam lobes and valve tappets. Oil, accumulating in the cam chamber sump, lubricates the lower camshaft bearing before being pumped through the closed looped circulatory system.
The United States patents described above are hereby expressly incorporated by reference in the description of the present invention.
Oil lubrication systems for engines typically require numerous and complex series of cast and drilled holes to provide lubrication oil passages to critical engine components, such as the crankshaft bearings of the engine. These cast and drilled holes are an expensive element of the engine""s manufacturing costs. Many of the oil passage holes must then be plugged where they break through an outside surface of the engine. Eliminating as many of these holes and passages as possible will reduce the overall cost and weight of the engine. Furthermore, the required plugs at the end of passages, where they break through an outside surface of the engine, also create an additional possibility of oil leakage. It would therefore be significantly beneficial if an oil lubrication circuit could be provided that minimizes the requirement for drilled and cast holes and passages within the cylinder block of the engine.
An engine made in accordance with the preferred embodiment of the present invention comprises a first shaft supported for rotation about a first axis within the engine. In addition, it comprises a conduit formed within the first shaft and extending along the first axis for at least a portion of the length of the first shaft. The liquid conduit has an inlet for conducting a liquid into the conduit and an outlet for conducting the liquid out of the conduit. The conduit comprises a first path and a second path, wherein the first and second paths extends in opposite directions generally parallel to the first axis of the first shaft.
The engine made in accordance with the present invention can further comprise a second shaft supported for rotation about a second axis within the engine. The first shaft is a camshaft and the second shaft is a crankshaft. A liquid pump is disposed within the body of the engine and in fluid communication between the first and second paths. The first and second paths can be concentric with each other and with the first axis. A tube is disposed within a central bore of the first shaft with the tube defining the first path within a central opening of the tube and the second path being defined between an outer cylindrical surface of the tube and an inner cylindrical surface of the central bore of the first shaft. The engine can be a powerhead of an outboard motor.